Valve system in an injection molding system

ABSTRACT

An injection molding apparatus including:
         a valve pin driven by an actuator, the valve pin extending axially through at least a portion of the channel length of the fluid flow channel, the fluid flow channel and the valve pin being configured or adapted such that the valve pin is movable axially upstream and downstream between an upstream position where the downstream flow of the injection fluid is restricted by a bulbous protrusion (B) of the pin being axially aligned (AL) with the throat (T) of the channel, an intermediate position where downstream flow of injection fluid is unrestricted (WG) and a fully downstream position where downstream flow of injection fluid is stopped at both the gate and at the throat.

RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityof U.S. application Ser. No. 15/788,099 filed Oct. 19, 2017 which is acontinuation of and claims the benefit of priority to U.S. applicationSer. No. 14/972,307 filed Dec. 17, 2015 which is a continuation of andclaims the benefit of priority to PCT/US15/061550 filed Nov. 19, 2015which claims priority to U.S. Provisional Application Ser. No.62/082,837 filed Nov. 21, 2014, the disclosures of which areincorporated by reference in their entirety as if fully set forth intheir entirety herein.

The disclosures of all of the following are incorporated by reference intheir entirety as if fully set forth herein: U.S. Pat. No. 5,894,025,6,062,840, 6,294,122, 6,309,208, 6,287,107, 6,343,921, 6,343,922,6,254,377, 6,261,075, 6,361,300 (7006), 6,419,870, 6,464,909 (7031),6,599,116, 7,234,929 (7075US1), 7,419,625 (7075US2), 7,569,169(7075US3), U.S. patent application Ser. No. 10/214,118, filed Aug. 8,2002 (7006), 7,029,268 (7077US1), (7077US2), 7,597,828 (7077US3), U.S.patent application Ser. No. 09/699,856 filed Oct. 30, 2000 (7056), U.S.patent application Ser. No. 10/269,927 filed Oct. 11, 2002 (7031), U.S.application Ser. No. 09/503,832 filed Feb., 15, 2000 (7053), U.S.application Ser. No. 09/656,846 filed Sep. 7, 2000 (7060), U.S.application Ser. No. 10/006,504 filed Dec. 3, 2001, (7068), U.S.application Ser. No. 10/101,278 filed Mar., 19, 2002 (7070) andinternational applications PCT/US2011/062099 and PCT/US2011/062096.

BACKGROUND OF THE INVENTION

Injection molding systems having fluid distribution valve systemsincluding proportional control valve systems have been employed ininjection molding systems used in a wide variety of environments andapplications where the valve systems including the fluid valvesthemselves and the fluid manifold that feeds the valve system is mountedoutside the hot half space or area of the injection molding systemswhere the heated fluid distribution hotrunner or manifold is mounted.Such systems as disclosed in international applicationsPCT/US2011/062099 and PCT/US2011/062096 purposely mount the actuators atan extended distance away from the heated manifold chamber or spacewithin the heated manifold is mounted or disposed in order to protectthe integrity of the valves and valve system generally. The valvesystems in such prior apparatuses cannot achieve an immediate, fast orquick movement response by the actuators in reaction to the supply ofdrive fluid the the proportional control valves that are interconnectedto the actuators, especially in the case of gas or pneumatic systems atleast because the overly long physical distance between thecommunication ports of the valve system and the fluid ports of theactuators prevents the fluid from providing an immediate response inmovement of the piston of the actuator.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an injection moldingapparatus (1000) comprising an injection molding machine (900), amanifold (21) that receives injection fluid (902) from the machine (900)and routes the injection fluid during the course of an injection cyclefrom an upstream end toward a downstream end of a fluid flow channel (54b) disposed in the manifold (21) or a nozzle (45) communicating (19)with the manifold (21), the fluid flow channel (45 b) having a flow axis(AX) and a channel length, the fluid flow channel communicating at thedownstream end with a gate (105) to a cavity (120) of a mold, theapparatus including:

a valve pin (40) driven by an actuator (30), the valve pin (40)extending axially through at least a portion of the channel length ofthe fluid flow channel (45 b), the valve pin having an upstream endinterconnected to the actuator and a downstream end (40 d), the valvepin being drivable by the actuator axially upstream and downstreamthrough the fluid flow channel,the fluid flow channel (45 b) including a throat (T) having an innercircumferential surface ((TS) having a selected throat configuration andthroat diameter (TD),the valve pin having bulbous portion (B) having an outer circumferentialsurface (OBS) and a bulb diameter (BD) adapted to interface with theinner circumferential surface (TS) of the throat (T) to enable arestricted degree of volume or velocity of flow of injection fluid (902)relative to a maximum degree of volume or velocity of flow when thebulbous portion (B) of the valve pin is axially aligned (AL) with thethroat (T),the valve pin (40) being drivable to a maximum downstream position wherea distal tip end (40 d) of the valve pin closes the gate (105) and stopsflow of the injection fluid (902) through the gate (105).

The actuator (40) is preferably driven by a valve assembly (10)comprised of a housing (20) and a spool (50) slidably mounted andcontrollably movable back and forth along an axis (A) within the housingbetween two or more drive fluid flow positions,

the spool (50) being mechanically driven by first and second actuatorsor solenoids (70 a, 70 b) that each separately engage the spool atopposing axial ends to effect movement of the spool (50) back and forthbetween the drive fluid flow positions.

The actuators or solenoids are preferably drivable in only one lineardirection and adapted such that the first solenoid or actuator drivesthe spool in a first linear direction and the second solenoid oractuator drives the spool in a second linear direction opposite thefirst linear direction, the first and second solenoids or actuatorsbeing drivable at different times such that the spool is driven by onlyone or the other of the first and second solenoids or actuators at anyone selected point in time.

The actuators or solenoids can be controllably energizable to drive thespool a distance or length of travel or at a velocity of travel that isproportional to the degree or amount of voltage, current or power thatis applied to the actuators or solenoids.

The bulbous portion of the valve pin typically has a diameter that isbetween about 0.01 and about 0.20 mm less than the throat diameter.

The fluid flow channel and the valve pin are preferably configured oradapted such that the valve pin is movable axially upstream anddownstream between an upstream position where the downstream flow of theinjection fluid is restricted by the bulb portion of the pin beingaxially aligned with the throat of the channel, an intermediate positionwhere downstream flow of injection fluid is unrestricted and a fullydownstream position where downstream flow of injection fluid is stoppedat both the gate and at the throat.

In the upstream position of the valve pin, the bulb portion ispreferably axially aligned with the throat, the valve pin including areduced diameter neck portion that aligns with the throat when the pinis in the intermediate position to enable unrestricted flow of theinjection fluid.

The valve pin can include an upstream portion configured or adapted tostop flow of injection fluid through the flow channel when the valve pinis in the fully downstream position.

The upstream position of the valve pin is typically a start position ata beginning of an injection cycle where the bulbous protrusion isaxially aligned with the throat, the bulbous protrusion and the throatbeing adapted to enable a restricted flow of the injection fluid from anupstream side of the bulbous protrusion to a downstream side of thebulbous protrusion that reduces tensile forces on the pin (40).

The upstream position of the valve pin is typically a start position ofthe valve pin at a beginning of an injection cycle where the bulbousprotrusion is axially aligned with the throat to restrict flow of theinjection fluid.

The actuator is preferably interconnected to a controller that includesa program that instructs the actuator to position the valve pin at thebeginning of the injection cycle such that the bulbous protrusion isaxially aligned with the throat.

The actuator is typically drivable at a rate of travel between zero anda maximum rate of travel, the actuator being interconnected to acontroller that includes a program that instructs the actuator to drivethe valve pin downstream from a start position to the maximum downstreamposition defining a stroke length, the program including instructionsthat instruct the actuator to drive the valve pin downstream at a rateof travel beginning from the start position along at least a portion ofthe stroke length that is less than the maximum rate of travel.

The bulbous portion and the throat are preferably configured or adaptedto enable a restricted flow of injection fluid that reduces a differencein pressure between fluid disposed upstream of the throat and fluiddisposed downstream of the throat when the bulbous portion and thethroat are axially aligned.

The bulbous portion and the throat are preferably configured or adaptedto enable a restricted flow of injection fluid that lowers a differencein pressure of injection fluid upstream of the throat and injectionfluid downstream of the throat when the bulbous portion and throat areaxially aligned to a level that reduces or eliminates a spike or peak inpressure of injection fluid at the gate above a selected maximumpressure.

In another aspect of the invention there is provided a method of forminga part by operation of an apparatus as described above comprisinginjecting an injection fluid from the injection molding machine into themanifold and controlling flow of the injection fluid into the cavity byuse of the controller such that the actuator is instructed to drive thevalve pin downstream from the start position to the gate closed positionat a rate of travel beginning from the start position along at least aportion of the stroke length that is less than the maximum rate oftravel.

In another aspect of the invention there is provided an injectionmolding apparatus (1000) comprising an injection molding machine (900),a manifold (21) that receives injection fluid (902) from the machine(900) and routes the injection fluid (902) during the course of aninjection cycle from an upstream end toward a downstream end of a fluidflow channel (45 b) disposed in the manifold (21) or a nozzle (45)communicating (19) with the manifold, the fluid flow channel having aflow axis (AX) and a channel length, the fluid flow channel (45 b)communicating at the downstream end with a gate (105) to a cavity (120)of a mold, the apparatus (1000) including:

a valve pin (40) driven by an actuator (30), the valve pin extendingaxially (AX) through at least a portion of the channel length of thefluid flow channel, the valve pin (40) having an upstream endinterconnected to the actuator and a downstream end (40 d), the valvepin being drivable by the actuator (30) axially upstream and downstreamthrough the fluid flow channel (45 b),the fluid flow channel including a throat (T) having an innercircumferential surface (TS) having a selected throat configuration andthroat diameter (TD),the fluid flow channel and the valve pin being configured or adaptedsuch that the valve pin (40) is movable axially upstream and downstreambetween an upstream position where the downstream flow of the injectionfluid is restricted by a bulb portion (B) of the pin being axiallyaligned (AL) with the throat (T) of the channel, an intermediateposition where downstream flow of injection fluid (902) is unrestricted(WG) and a fully downstream position where downstream flow of injectionfluid is stopped at both the gate (105, 40 d) and at the throat (TS,UES, UPD, TD).

The actuator is typically driven by a valve assembly (10) comprised of ahousing (20) and a spool (50) slidably mounted and controllably movableback and forth along an axis (A) within the housing between two or moredrive fluid flow positions,

the spool (50) being mechanically driven by first and second actuatorsor solenoids (70 a, 70 b) that each separately engage the spool atopposing axial ends to effect movement of the spool back and forthbetween the drive fluid flow positions.

The actuators or solenoids (70 a, 70 b) are preferably drivable in onlyone linear direction and adapted such that the first solenoid oractuator drives the spool in a first linear direction (70 ad) and thesecond solenoid or actuator drives the spool in a second lineardirection (70 bd) opposite the first linear direction (70 ad), the firstand second solenoids or actuators being drivable at different times suchthat the spool is driven by only one or the other of the first andsecond solenoids or actuators at any one selected point in time.

The actuators or solenoids are preferably controllably energizable todrive the spool a distance or length of travel or at a velocity oftravel that is proportional to the degree or amount of voltage, currentor power that is applied to the actuators or solenoids.

The upstream position of the valve pin is typically a start position ata beginning of an injection cycle where the bulbous protrusion isaxially aligned with the throat, the bulbous protrusion and the throatbeing adapted to enable a restricted flow of the injection fluid from anupstream side of the bulbous protrusion to a downstream side of thebulbous protrusion that reduces tensile forces on the pin (40).

In another aspect of the invention there is provided, an injectionmolding apparatus (1000) comprising an injection molding machine (900),a manifold (21) that receives injection fluid (902) from the machine androutes the injection fluid during the course of an injection cycle froman upstream end toward a downstream end of a fluid flow channel (45 b)disposed in the manifold or a nozzle communicating with the manifold,the fluid flow channel (45 b) having a flow axis (AX) and a channellength, the fluid flow channel communicating at the downstream end witha gate (105) to a cavity (120) of a mold, the apparatus (1000)including:

a valve pin (40) driven by an actuator (30), the valve pin extendingaxially through at least a portion of the channel length of the fluidflow channel, the valve pin being drivable between a downstream gateclosed position, an upstream gate open position where injection fluidflows freely through the gate,the actuator being interconnected to and driven by a valve assembly (10)comprised of a housing (20) and a spool (50) slidably mounted andcontrollably movable back and forth along an axis (A) within the housingbetween two or more drive fluid flow positions,the spool being mechanically driven by first and second actuators orsolenoids (70 a, 70 b) that each separately engage the spool at opposingaxial ends to effect movement of the spool back and forth (70 ad, 70 bd)between the drive fluid flow positions,the first and second actuators or solenoids being drivable in only onelinear direction (70 ad, 70 bd) and adapted such that the first solenoidor actuator (70 a) drives the spool in a first linear direction and thesecond solenoid or actuator (70 bd) drives the spool in a second lineardirection opposite the first linear direction, the first and secondsolenoids or actuators being drivable at different times such that thespool is driven by only one or the other of the first and secondsolenoids or actuators at any one selected point in time.

The actuators or solenoids are preferably controllably energizable todrive the spool a distance or length of travel or at a velocity oftravel that is proportional to the degree or amount of voltage, currentor power that is applied to the actuators or solenoids.

The fluid flow channel typically includes a throat having an innercircumferential surface having a selected throat configuration andthroat diameter,

the valve pin having bulbous portion having an outer circumferentialsurface (OBS) and a bulb diameter adapted to interface with the innercircumferential surface of the throat to enable a restricted degree ofvolume or velocity of flow of injection fluid relative to a maximumdegree of volume or velocity of flow when the bulbous portion of thevalve pin is axially aligned with the throat,the valve pin being drivable to a maximum downstream position where adistal tip end of the valve pin closes the gate and stops flow of theinjection fluid through the gate.

The fluid flow channel and the valve pin are typically configured oradapted such that the valve pin is movable axially upstream anddownstream between an upstream position where the downstream flow of theinjection fluid is restricted by the bulb portion of the pin beingaxially aligned with the throat of the channel, an intermediate positionwhere downstream flow of injection fluid is unrestricted and a fullydownstream position where downstream flow of injection fluid is stoppedat both the gate and at the throat.

The bulbous portion and the throat are preferably configured or adaptedto enable a restricted flow of injection fluid that reduces a differencein pressure between fluid disposed upstream of the throat and fluiddisposed downstream of the throat when the bulbous portion and thethroat are axially aligned.

The bulbous portion and the throat are preferably configured or adaptedto enable a restricted flow of injection fluid that lowers a differencein pressure of injection fluid upstream of the throat and injectionfluid downstream of the throat when the bulbous portion and throat areaxially aligned to a level that reduces or eliminates a spike or peak inpressure of injection fluid at the gate above a selected maximumpressure.

The first and second solenoids or actuators are preferablyinterconnected to and controllably driven by a controller containing aprogram that instructs the first and second solenoids or actuators todrive the spool to selected ones of the two or more drive fluidpositions that cause the actuator to drive the valve pin from thedownstream gate closed position to the upstream gate open positiondefining a stroke length at one or more predetermined rates of travelover the course of travel of the valve pin along the stroke length.

The first and second solenoids are preferably interconnected to andcontrollably driven by a controller containing a program that instructsthe first and second solenoids to drive the spool to selected ones ofthe two or more drive fluid positions that cause the actuator to drivethe valve pin from the downstream gate closed position to the upstreamgate open position defining a stroke length at a rate of travelbeginning from the start position along at least a portion of the strokelength that is less than the maximum rate of travel.

The actuators or solenoids are preferably controllably energizable todrive the spool a distance or length of travel or at a velocity oftravel that is proportional to the degree or amount of voltage, currentor power that is applied to the actuators or solenoids.

In another aspect of the invention there is provided a method of forminga part by operation of an apparatus as described above comprisinginjecting an injection fluid from the injection molding machine into themanifold and controlling flow of the injection fluid into the cavity byuse of the controller to actuate the first and second solenoid atdifferent times over the course of the injection cycle such that thespool is driven by only one or the other of the first and secondsolenoids at any one selected point in time.

In another aspect of the invention there is provided an injectionmolding apparatus comprising an injection molding machine, a manifoldthat receives injection fluid from the machine and routes the injectionfluid during the course of an injection cycle from an upstream endtoward a downstream end of a fluid flow channel disposed in the manifoldor a nozzle communicating with the manifold, the fluid flow channelhaving a flow axis and a channel length, the fluid flow channelcommunicating at the downstream end with a gate to a cavity of a mold,the apparatus including:

a valve pin driven by an actuator, the valve pin extending axiallythrough at least a portion of the channel length of the fluid flowchannel, the valve pin having an upstream end interconnected to theactuator, a downstream end movable by the actuator between a gate closedposition and an upstream gate open position where fluid flows freelythrough the gate, the valve pin including a bulbous protrusion disposedbetween the upstream end and the downstream end,the fluid flow channel including a throat having an innercircumferential surface having a selected throat configuration andthroat diameter,the bulbous protrusion having an outer circumferential surface (OBS)having a bulb configuration that is complementary to the throatconfiguration and a bulb diameter, the actuator being adapted tocontrollably drive the valve pin between a downstream gate closedposition where the pin prevents injection fluid from flowing through thegate, an upstream gate open position where injection fluid flows freelythrough the gate and an intermediate maximum flow restriction positionwhere the outer surface of the bulbous protrusion is disposed in anaxial alignment position with the throat, the bulb diameter and thethroat diameter being selected such that a gap is formed between theouter circumferential surface of the bulbous protrusion and the innercircumferential surface of the throat that enables flow of injectionthrough the gate at a flow rate that relieves pressure in the injectionfluid upstream of the throat section.

The gap that is formed between the outer circumferential surface of thebulbous protrusion and the inner circumferential surface of the throatis preferably between about 0.05 mm and about 0.20 mm.

The valve pin is typically disposed in a start position at the beginningof the injection cycle such that the bulbous protrusion is disposed inor near the axial alignment position with the throat.

The actuator is preferably interconnected to a controller that includesa program that instructs the actuator to position the valve pin at thebeginning of the injection cycle such that the bulbous protrusion isdisposed in or near the axial alignment position with the throat.

The actuator is drivable at a rate of travel between zero and a maximumrate of travel, the actuator being interconnected to a controller thatincludes a program that instructs the actuator to drive the valve pindownstream from the start position to the gate closed position defininga stroke length, the program including instructions that instruct theactuator to drive the valve pin downstrream at a rate of travelbeginning from the start position along at least a portion of the strokelength that is less than the maximum rate of travel.

In another aspect of the invention there is provided a method of forminga part by operation of the apparatus described immediately above, themethod comprising injecting an injection fluid from the injectionmolding machine into the manifold and controlling flow of the injectionfluid into the cavity by use of the controller such that the actuator isinstructed to drive the valve pin downstream from the start position tothe gate closed position at a rate of travel beginning from the startposition along at least a portion of the stroke length that is less thanthe maximum rate of travel.

In another aspect of the invention there is provided an injectionmolding apparatus comprising an injection molding machine, a manifoldthat receives injection fluid from the machine and routes the injectionfluid during the course of an injection cycle from an upstream endtoward a downstream end of a fluid flow channel disposed in the manifoldor a nozzle communicating with the manifold, the fluid flow channelhaving a flow axis and a channel length, the fluid flow channelcommunicating at the downstream end with a gate to a cavity of a mold,the apparatus including:

a valve pin driven by an actuator, the valve pin extending axiallythrough at least a portion of the channel length of the fluid flowchannel, the valve pin being drivable between a downstream gate closedposition, an upstream gate open position where injection fluid flowsfreely through the gate,the actuator being driven by a valve assembly comprised of a housing anda spool slidably mounted and controllably movable within the housingbetween two or more drive fluid flow positions,the spool being mechanically driven by first and second controllablydriven plungers or pistons that each separately engage the spool atopposing axial ends to effect movement of the spool between the drivefluid flow positions, the plungers or pistons being driven that thefirst plunger or piston drives the spool in a first linear direction andthe second plunger or piston drives the spool in a second lineardirection opposite the first linear direction, the first and secondplungers or pistons always being driven at different times such that thespool is driven by only one or the other of the first and secondsolenoids at any selected point in time.

The first and second plungers or pistons are preferably driven by asolenoid that is controllably energizable to drive the plungers orpistons in the first and second linear directions at predetermined timesand preselected rates of travel over the course of the injection cycle.

The first and second plungers or pistons are preferably interconnectedto and controllably driven by a controller containing a program thatinstructs the first and second plungers or pistons to drive the spool toselected ones of the two or more drive fluid positions that cause theactuator to drive the valve pin between the downstream gate closedposition and the upstream gate open position defining a stroke length,the valve pin being driven at one or more predetermined rates of travelover the course of travel of the valve pin along the stroke length.

The first and second plungers or pistons can be interconnected to andcontrollably driven by a controller containing a program that instructsthe first and second plungers or pistons to drive the spool to selectedones of the two or more drive fluid positions that cause the actuator todrive the valve pin from the downstream gate closed position to theupstream gate open position defining a stroke length, the valve pinbeing driven along one or more predetermined profiles of pin positionover the course of travel of the pin along the stroke length.

The first and second plungers or pistons can be interconnected to andcontrollably driven by a controller containing a program that instructsthe first and second plungers or pistons to drive the spool to selectedones of the two or more drive fluid positions that cause the actuator todrive the valve pin from the downstream gate closed position to theupstream gate open position defining a stroke length, the valve pinbeing driven at a rate of travel beginning from the start position alongat least a portion of the stroke length that is less than the maximumrate of travel.

In another aspect of the invention there is provided a method of forminga part by operation of the apparatus described immediately above, themethod comprising injecting an injection fluid from the injectionmolding machine into the manifold and controlling flow of the injectionfluid into the cavity by use of the controller to actuate the first andsecond solenoid at different times over the course of the injectioncycle such that the spool is driven by only one or the other of thefirst and second plungers or pistons at any selected point in time.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1A is a schematic view of one embodiment of a proportionaldirectional control valve component for use in an apparatus according tothe invention.

FIG. 1B is a side cross-sectional view of one embodiment of aproportional directional control valve component for use in an apparatusaccording to the invention.

FIG. 1C is a side schematic sectional view of another embodiment of aproportional directional control valve component for use in an apparatusaccording to the invention.

FIG. 1D is a side schematic sectional view of an injection moldingapparatus or system according to the invention incorporating anotherembodiment of a proportional directional control valve component useablein an apparatus according to the invention.

FIG. 2 is an exemplary plot of valve pin position versus time using onepreferred embodiment of a valve in an apparatus according to theinvention.

FIG. 3 is a schematic representation of one embodiment of interconnectedvalve, actuator, valve pin configuration and electronic controllercomponents in an apparatus according to the invention where thecontroller uses a real time signal indicative of pin position as thebasis for a controller program that controls driven position or velocityof the valve pin.

FIG. 4 is a schematic representation of another embodiment ofinterconnected valve, actuator, valve pin configuration and electroniccontroller components in an apparatus according to the invention wherethe controller uses a real time signal indicative of pin position as thebasis for a controller program that controls driven position or velocityof the valve pin.

FIG. 5A is a side cross-sectional view of a preferred valve withpreferred valve pin configuration components for use in an apparatusaccording to the invention showing the valve pin disposed at a startposition or starting point of an injection cycle.

FIG. 5B is a side sectional view of the FIG. 5A components showing thevalve pin disposed at an intermediate downstream gate open positionsubsequent to the starting point or time of an injection cycle.

FIG. 5C is a side sectional view of the FIG. 5A components showing thevalve pin disposed at a gate closed downstream position at the end of aninjection cycle.

FIG. 6 is an exemplary plot of a drop in injection fluid pressurelocated within the nozzle of a valve having a configuration as shown inFIGS. 5A-5C versus position of the valve pin, the zero position of thevalve pin being the position shown in FIG. 5A.

FIG. 7 is a schematic of a system according to the invention using areal time signal indicative of cavity pressure as the basis for acontroller program that controls driven position or velocity of thevalve pin.

DETAILED DESCRIPTION

FIGS. 1A, 1B show one embodiment of a drive fluid valve assembly 10element of an injection molding system 1000 according to the invention.The valve assembly 10 is comprised of a valve housing 20 having a spool50 similar to a spool as shown and described in FIG. 28 of U.S.publication 20020086086, the disclosure of which is incorporated hereinby reference in its entirety as if fully set forth herein. In the FIGS.1A, 1B configuration the spool or spool assembly 50 is controllablyreciprocally driven back and forth BF by a controller 100 along axis Ato route drive fluid (preferably hydraulic liquid such as oil) to andfrom the drive chambers of a fluid driven actuator 30 that isinterconnected to a valve pin 40.

Precise control over the piston or other moving component of a fluiddriven actuator such as actuator 30, FIGS. 1A, 1B, 1C or actuator 322 a,FIG. 1D, can be more effectively carried out with a proportionallydirectionally driven valve 50, 370 as shown in FIGS. 1A-1D. Aproportional or proportionally directionally driven valve 50, 370 asused herein is a valve having a moving member such as a spool that isdriven by and travels a distance that is proportional to the amount ordegree of electrical voltage, power, current or energy that is appliedto the drive mechanism such as a solenoid that is interconnected to anddrives the moving member of the valve.

The spool assembly 50, FIGS. 1A-1C, (370, FIG. 1D) is controllablydrivable back and forth BF (374, 375) along a linear travel path A byengagement or interconnection to a pair of opposing solenoid drivenactuators 70 a, 70 b that are controllably driven such that eachseparate actuator 70 a, 70 b only drives the solenoid in one direction70 ad, 70 bd always at separate times that are controlled by controller100. The actuators or solenoids 70 a, 70 b most preferably are adaptedto drive the spool in their respective one direction 70 ad, 70 bd along,to or along a length or distance of travel or a magnitude of velocitythat is proportional to one or more of electrical voltage, current orpower that is applied to the electric drive mechanism such as a solenoidthat is interconnected to and drivably moves the spool 50. In oneembodiment of the present invention two separate drive mechanisms suchas the two solenoids or actuators 70 a, 70 b are interconnected to anddrive the spool in one direction only, the controller 100 that directsthe drive of the actuators or solenoids being adapted to enable thedriving of only one of the two actuator 70 a, 70 b at a single time.

The controller 100 is also provided with a program that includesinstructions and predetermined data such as a profile of pin positiondata that instruct the actuators or solenoids 70 a, 70 b to be drivenaccording to a predetermined degree of input of electrical voltage,current or power at predetermined times over the course of an injectioncycle so as to position the pin 40 at positions that match apredetermined profile of preferred pin positions over the course of aninjection cycle.

The spool 50 is typically centered within the axial center of thehousing such that the heads and recesses of the spool 50 are properlypositioned for opening and closing fluid flow ports provided in thevalve housing 20, the ports being drive fluid flow sealably connected tothe upstream and downstream drive chambers of the actuator 30.

One configuration embodiment of a spool assembly 50 is shown in FIG. 1Cwhich includes a spool 700 having heads 540, 550, 560 with respectiveouter circumferential head surfaces HS1, HS2, HS3. A fluid seal such asan O-ring or the equivalent can be disposed between the head surfacesHS1, HS2, HS3 and the interior interface surfaces CS of the cylinder 505so as to seal the recesses R1, R2 disposed between the heads againstfluid flow between the recesses.

Alternatively, the respective interior interface surfaces CS of thecylinder 505 can be machined to close tolerances so as to form a microgap at the interfaces IS between the head surfaces HS1, HS2, HS3 of eachhead and the adjacent opposing surface of the interior wall surface CSof the cylinder 505 in the range of 1 to 10 micrometers, therebyavoiding the need for the use of a separate fluid seal, such as apolymeric layer of material such as a film or O-ring, at or between theinterfaces IS of such surfaces. Such avoidance of the use of separatefluid seals at the interfaces IS reduces friction at the interfaces andenables the spool 700 to respond more quickly to force that is appliedby drive mechanisms 70 a, 70 b that drives the spool to travel laterallyBF along axis A.

The spool 700 is preferably controllably driven back and forth BF alongaxis A by the pair of opposing solenoid driven actuators 70 a, 70 b thatare controllably driven by controller 100 that includes a program havinginstructions that control the solenoid driven actuators to drive thespool 700 such that each separate actuator 70 a, 70 b only drives thesolenoid and the interconnected shaft of the spool 700 in one direction70 ad, 70 bd always at separate times in one direction, either 70 ad or70 bd. The spool 700 is typically centered within the axial center ofthe housing 50 a such that the heads and recesses of the spool 700 areproperly positioned for opening and closing fluid flow ports CP1, CP2provided in the valve housing 50 a, the ports being drive fluid flowsealably connected to the upstream and downstream drive chambers of theactuator 30.

As shown in FIG. 1C, the valve assembly 500 comprises a spool valvemember 700 comprised of and configured in the form of an axial rod orshaft 702, heads 540, 550, 560, recesses R1, R2 disposed between theheads and a sealed cylinder 505. The spool valve member 700 is slidablydrivable within the interior of the cylinder 505, the interior wallsurface CS of the cylinder 505 being formed to have a diameteressentially the same as the outside diameter of the outercircumferential surfaces HS1, HS2, HS3 of the heads 540, 550, 560respectively. The outside surfaces HS1, HS2, HS3 of the heads 540, 550,560 can be integral with each other such that there is no other materialdisposed between the heads 540, 550, 560 and the interfaces of surfacesHS1, HS2, HS3 and the interior wall surface CS of the cylinder 505 toform a seal against flow of pressurized gas along or through theinterfaces.

The spool valve member 700 is drivable LS laterally back and forth Lalong its axis A and depending on the precise lateral position BF of themember 700. The precise lateral BF position of the heads 540, 550, 560relative to the flow ports or apertures CP1, CP2 in the cylinder housing504, 505 determines the direction and degree of flow of pressurizedfluid back and forth 200, 300 to and from the drive chambers 32, 34 ofthe actuator 30. Further depending on the precise lateral BF positioningof the spool valve member 700 pressurized fluid will vent or evacuatethrough one of two vents V1, V2 to a reservoir of fluid 120 such as atank of fluid or in the case of a pneumatic system ambient air.

FIG. 1D shows a more detailed arrangement and interconnection ofcomponents of an entire injection molding system 1000 according to theinvention. As shown an injection molding machine 900 feeds pressuredinjection fluid 902 into a distribution channel 19 of a heated manifoldor hotrunner 21 on which an actuator 322 a is mounted and through whichthe valve pin 41 extends. As discussed in greater detail herein thevalve pin 40 is controllably drivable to open and close a gate 105 tothe cavity 120 of a mold.

With reference to the system shown in FIG. 1D, the drive fluid for theactuator 322 a may be supplied by a common manifold or fluid feed duct358 a. Such common fluid feed ducts are most preferably independent ofthe fluid driven actuators, i.e. the ducts do not comprise a housingcomponent of the actuators but rather the actuators have a selfcontained housing, independent of the fluid feed manifold 358 a, whichhouses a sealably enclosed cavity in which a piston is slidably mounted.For example, as shown in FIG. 1D, the fluid input/output ports 350 a,352 a of independent actuator 322 a are sealably mated with the fluidinput output ports 354 a, 356 a of a fluid manifold 358 a which commonlydelivers actuator drive fluid (such as oil or air) to the sealed drivechambers 336 a, 338 a of actuator 322 a. Most preferably, the ports 354a, 356 a of the manifold 358 a are sealably mated with theircomplementary actuator ports 350 a, 352 a via compression mating of theundersurface 360 of the manifold 358 a) with the upper surface 341 ofthe actuator 322 a. As can be readily imagined a plurality of actuatorsmay also utilize a manifold plate which forms a structural component ofone or more of the actuators and serves to deliver drive fluid commonlyto the actuators, e.g. the manifold plate forms a structural wallportion of the housings of the actuators which serves to form the fluidsealed cavity within which the piston or other moving mechanism of theactuator is housed.

In the FIG. 1D embodiment, a separate proportional valve 370 for eachindividual actuator 322 a is mounted on a common drive fluid deliverymanifold 358 a. The manifold 358 a has a single pressurized fluiddelivery duct 372 which feeds pressurized drive fluid first into thedistributor cavity 370 a of the valve 370. The pressurized fluid fromduct 372 is selectively routed via left 375 or right 374 movement ofplunger or spool 380 either through port 370 b into piston chamber 338 aor through port 370 c into piston chamber 336 a. The plunger or spool380 is controllably movable to any left to right 375, 374 (BF) positionwithin sealed housing 381 via drives 70 a, 70 b which receives controlsignals 382 from the controller or CPU 100. The drivers 70 a, 70 btypically comprise an electrically driven mechanism such as a solenoiddrive, linear force motor or permanent magnet differential motor whichis, in turn, controlled by and interconnected to CPU or controller 100via interface 384 which interprets and communicates control signals fromthe CPU 100 to the servo drivers 70 a, 70 b. Restrictors or projections370 d and 370 g of plunger/spool 380 are slidable over the portapertures 370 b and c to any desired degree such that the rate of flowof pressurized fluid from chamber 370 a through the ports can be variedto any desired degree by the degree to which the aperture ports 370 b,370 g are covered over or restricted by restrictors 370 d, 370 g. Thevalve 370 includes left and right vent ports which communicate withmanifold fluid vent channels 371, 373 respectively for ventingpressurized fluid arising from the left 375 or right 374 movement of theplunger/spool 380. Thus, depending on the precise positioning ofrestrictors 370 d and 370 g over apertures 370 b and 370 c, the rate anddirection of axial movement of piston 385 and pin 40 can be selectivelyvaried and controlled which in turn controls the rate of melt materialfrom manifold channel 19 through a nozzle bore or channel 45 b formedaxially through the body 45 c of a nozzle 45 and gate 105, FIGS. 3,5A-5C.

FIG. 2 shows a typical plot of pin position versus time for a valve asshown in FIGS. 5A-5C.

FIG. 3 shows a system where the valve 30, 40, 45 comprises a valve pin40 that is cylindrical along its axial length the distal tip end 40 d ofwhich controls injection fluid flow through the gate 105 into the cavity120 by controlled positioning of the tip end 40 d relative to theinterior surface 110 of the gate 105 by use of a proportionaldirectional control valve such as described with reference to FIGS. 1A,1B, 1C, 1D, 2.

FIG. 4 shows an alternative system with advanced melt control capabilityby virtue of the use of a valve 30, 40, 45 configuration where thecentral flow channel 45 b of a nozzle 45 and valve pin 40 have aconfiguration as shown in FIGS. 5A, 5B, 5C that include a bulb orwidened diameter portion B of the pin 40 together with a narrowed neck Nportion and a complementary throat section T of the nozzle channel 45 bconfigured relative to the neck N of the pin 40 to enable anunrestricted flow when neck N is aligned with throat T and a restricteddegree of flow of fluid 902 at a predetermined volume or velocity thatis less than the volume or velocity of an unrestricted or free flow whenthe bulb portion B is aligned with the throat T.

As shown in the FIGS. 4, 5A-5C embodiment, the nozzle 45 has a centralnozzle channel 45 b that terminates downstream in a gate 105 that mateswith a mold cavity 120. The nozzle channel 45 b has a throat or throatsection T disposed upstream from the gate 105 that has a narrowed indiameter interior throat surface TS extending an axial length AL at andalong a selected intermediate upstream section of the nozzle channel 45b. Further upstream from the throat section T the nozzle channel 45 bhas an upstream section US that widens in diameter relative to thethroat section T as well as the gate 105. The throat diameter TD of thethroat surface TS is narrower or less than the diameters of the interiorsurfaces of the nozzle channel 45 b that are disposed immediatelyupstream UIS and immediately downstream DIS of the throat surface TS.The inner circumferential surface of the throat TS has a selected throatconfiguration, contour or shape and has a preselected throat diameterTD.

The valve pin 40 shown in the FIGS. 5A-5C embodiment is configured tohave a narrowed neck or neck portion N that has a diameter that issignificantly less than the diameter TD of the throat portion of thenozzle channel 45 b such that when the neck portion N is axially alignedwith the axial length AL of the nozzle channel 45 b a widened gap WG isformed between the outer circumferential surface NS of the neck N andthe inner surface TS of the throat T which enables open free, fullvelocity flow of the injection fluid material 902 through the widenedgap WG downstream toward and through the gate 105. The diameter of theneck portion is typically between about 2 mm and about 4 mm.

The valve pin 40 has an upstream portion UPS disposed upstream of theneck portion N. Downstream of the neck portion N, the valve pin has abulb or bulbous portion B that has an outer circumferential bulb surfaceOBS that has configuration that is complementary to the configuration ofthe inner throat surface TS in axial length AL and shape generally. Themaximum diameter of the surface OBS is typically less than the diameterUPD of the upstream portion UPS of the valve pin 40.

The maximum diameter of the surface OBS is also slightly less than thediameter TD of the throat surface TS such that when the bulb surface OBSis axially AX aligned with the axial length AL of the throat surface TSa restriction gap G is formed between the bulb surface OBS and thethroat surface TS such that a relatively small amount of flow ofinjection fluid 902 that is less than full unrestricted flow is enabledto flow downstream through the channel 45 b and through the gap. The gapG is between the bulb surface OBS and the throat surface TS when thesurfaces OBS and TS are axially aligned is typically between about 0.05and about 0.20 mm.

The diameter UPD of the upper section of the valve pin 40 is typicallythe same or about the same as the diameter TD of the throat T such thatwhen the surfaces TS and UES mate, flow of injection fluid 902 throughchannel 45 b is stopped.

The actuator 30 is preferably adapted to controllably drive the valvepin 40 between a downstream gate closed position, FIG. 5C, where the pin40 prevents injection fluid from flowing through the gate either viaclosing off the gate 105 by mating of distal end pin surface 40 ds withthe interior surface 110 gs of the gate 105 or via mating of theexterior surface UES of the upstream end portion 40 u of the upstreamportion UPS of the pin 40 with the throat surface TS, the upstream end40 u having a diameter UPD that is the same or about the same as thediameter TD of the throat T such that when the surfaces TS and UES mateflow of injection fluid is stopped.

Thus the nozzle channel 45 b and the valve pin 40 are configured andadapted such that the pin 40 is movable axially upstream and downstreambetween positions where the valve pin 40 can be disposed in or driven toan upstream position such as shown in FIG. 5A where the downstream flowof injection fluid 902 is restricted by the bulb portion B of the pinbeing axially aligned with the narrow diameter throat portion T of thechannel, and subsequently the pin 40 can be disposed in or driven to anintermediate downstream position such as shown in FIG. 5B where thedownstream flow of injection fluid 902 is unrestricted and subsequentlythe pin 40 can be disposed in or driven to a fully downstream positionas shown in FIG. 5C where the downstream flow of injection fluid isstopped at both the gate 105 and at the upstream position of the throatT by an upstream portion UPS of the pin 40 being axially aligned withthe throat T. In the upstream position of the valve pin 40 when the bulbportion B is axially aligned with the throat T, a reduced volume orvelocity of downstream flow of injection fluid 902 is enabled. The bulbportion N and the throat portion T are adapted to enable a restricteddegree of downstream flow of fluid 902 at a predetermined volume orvelocity that is less than the volume or velocity of an unrestricted orfree flow that occurs when the neck portion N is axially aligned withthe throat portion T of the channel 45 b.

FIG. 5B shows the pin 40 in an intermediate axial downstream gate openposition where the bulb portion B is axially aligned with the throatportion T and injection fluid 902 flows freely through the widened gapWG and the gate 105 without restriction from interaction between theouter circumferential surfaces of the pin 40 and inner surfaces 45 s ofthe nozzle channel 45 b.

In the FIG. 5A position, the pin 40 is disposed in an start of cycle orupstream flow restriction position where the outer surface OBS of thebulbous protrusion B is disposed in an axial alignment position with theaxial length AL of the throat surface TS such that a flow restrictiongap G having a size of typically between about 0.05 and 0.2 mm is formedbetween the outer circumferential surface OBS of the bulbous protrusionB and the inner circumferential surface TS of the throat T. The bulb Band the throat T are selectively configured such that the gap G isrendered large enough to enable a predetermined small amount of flow ofinjection fluid 902 through the gate at a predetermined relatively smallor minimal flow rate that reduces the difference in fluid pressurebetween the upstream interior volume UIFP of the channel 45 b and thedownstream interior volume DIFP of the channel 45 b.

At the beginning or at the start of an injection cycle using a valveconfiguration as shown in FIGS. 5A-5C, the pin 40 is disposed in theaxial position shown in FIG. 5A. In the FIG. 5A start position, theinjection fluid 902 immediately upstream of the bulb B and throat T hasa pressure IFP that is at a maximum at a time immediately before the pinis moved downstream. The gap G is rendered large enough to reduce thepressure UIFP enough to cause a reduction in the difference in pressurebetween the upstream pressure UIFP of fluid 902 that is immediatelyupstream of the throat T and the downstream pressure DIFP of injectionfluid 902 that is disposed immediately downstream of the throat T whenthe bulb B and throat T are axially aligned. This reduction indifference between pressures UIFP and DIFP results in a similarreduction in difference or “drop” in pressure between UIFP and DIFP whenand during the course of travel of the valve pin from the position inFIG. 5A to the position in FIG. 5C.

FIG. 6 shows plots of the difference or drop in UIFP and DIFP as canexist using a valve according to the invention as shown for example inFIGS. 5A-5C that provides a small flow gap G, pressure difference plotAVP, versus the difference in upstream volume pressure USFB anddownstream volume pressure DSFB when using a prior art valve that has afootball-like FSB, FV configuration. FIG. 6 illustrates pressuredifference plot FVP, where the outer surface FBS of an upstream footballconfigured bulb FSB mates with the inner surface FTSF of the narrowedthroat of the nozzle channel 45 b in the start or upstream position FSPof the valve pin 40 and completely closes off or stops injection fluidflow in the start position FSP as shown in FIG. 6. When the footballconfigured FSB pin 40 is subsequently driven downstream FIP from thestart position FSP, injection fluid initially flows downstream from theupstream side of the football USFB to the downstream side of thefootball DSFB at a higher rate than it flows using the pin configurationAV of the present invention as described with reference to FIGS. 5A, 5B,5C. Such a prior art football shaped or configured bulb and nozzlechannel configuration are described in U.S. publication 20020086086(such as shown in FIGS. 28, 29, 32 et seq.) the disclosure of which isincorporated herein by reference in its entirety. As shown in FIG. 6 bythe difference between the plots AVP and FVP in FIG. 6, the lesser dropin pressure as between UIFP and DIFP (plot AVP versus plot FVP) when thepin is initially moved from the start position ASP to the intermediateposition AIP reduces pressure spikes at the gate thus reducing theoccurrence of haze or artifacts in the molded part at the position ofthe gate, and generally provides a smoother transition in flow ofinjection fluid from the upstream volume side UIFP to the downstreamvolume side DIFP of the flow of injection fluid 902. The smallerdifference in pressure between the upstream side UIFP and the downstreamside DIFP of the throat T creates less of a rush or a lesser velocity offlow injection fluid through gate 105 when the pin 40 is initially moveddownstream beginning from the starting position as in FIG. 5A, plot AVP.And the AV configuration creates a generally more even pressuredifference between fluid on the upstream side UIFP and the downstreamside DIFP. As a comparison of plots FVP and AVP show, a higher rush orvelocity of flow of fluid 902 through the gate 105 occurs when a priorart football FSP configured pin 40, FIG. 6, is initially moveddownstream from a start of injection cycle upstream position FSP towarda downstream end of cycle gate closed position FEP, plot FVP.

The less extreme difference between upstream and downstream injectionfluid 902 pressures as shown by plot AVP using the AV configured pin andchannel configuration 45 b of FIGS. 5A-5C also allows for injectionfluid pressure to go past the area of the throat T restriction and acton the opposing downstream face of the bulbous portion B of the valvepin 40, reducing tensile forces on the pin 40 which enables a lower costpin because strength requirements do not need to account for a fullpressure build-up on the upstream side of the bulbous portion B.

What is claimed is:
 1. An injection molding apparatus comprising aninjection molding machine, a manifold that receives injection fluid fromthe machine and routes the injection fluid during the course of aninjection cycle from an upstream end toward a downstream end of a fluidflow channel disposed in the manifold or a nozzle communicating with themanifold, the fluid flow channel having a flow axis (AX) and a channellength, the fluid flow channel communicating at the downstream end witha gate to a cavity of a mold, the apparatus including: a valve pindriven by an actuator, the valve pin extending axially (AX) through atleast a portion of the channel length of the fluid flow channel, thevalve pin having an upstream end interconnected to the actuator and adownstream end, the valve pin being drivable by the actuator axiallyupstream and downstream through the fluid flow channel, the fluid flowchannel including a throat (T) having an inner circumferential surface(TS) having a selected throat configuration and throat diameter (TD),the fluid flow channel and the valve pin being configured or adaptedsuch that the valve pin is movable axially upstream and downstreambetween an upstream position where the downstream flow of the injectionfluid is restricted by a bulbous protrusion (B) of the pin being axiallyaligned (AL) with the throat (T) of the channel, an intermediateposition where downstream flow of injection fluid is unrestricted (WG)and a fully downstream position where downstream flow of injection fluidis stopped at both the gate and at the throat, wherein the valve pin isadapted to be disposed in a start of cycle or upstream flow restrictionposition such that a flow restriction gap (G) is formed between an outercircumferential surface (OBS) of the bulbous protrusion (B) and theinner circumferential surface (TS) of the throat (T) that is largeenough to enable a predetermined small amount of flow of injection fluidthrough the gate that reduces a difference in fluid pressure between anupstream interior volume (UIFP) of the channel and a downstream interiorvolume (DIFP) of the channel.
 2. The apparatus of claim 1 wherein: theactuator is driven by a valve assembly comprised of a housing and aspool slidably mounted and controllably movable back and forth along anaxis (A) within the housing between two or more drive fluid flowpositions, the spool being mechanically driven by first and secondactuators or solenoids that each separately engage the spool at opposingaxial ends to effect movement of the spool back and forth between thedrive fluid flow positions.
 3. The apparatus of claim 1 wherein thefirst and second actuators or solenoids are drivable in only one lineardirection and adapted such that the first solenoid or actuator drivesthe spool in a first linear direction and the second solenoid oractuator drives the spool in a second linear direction opposite thefirst linear direction, the first and second solenoids or actuatorsbeing drivable at different times such that the spool is driven by onlyone or the other of the first and second solenoids or actuators at anyone selected point in time.
 4. The apparatus of clam 1 wherein the firstand second actuators or solenoids are controllably energizable to drivethe spool a distance or length of travel or at a velocity of travel thatis proportional to the degree or amount of voltage, current or powerthat is applied to the actuators or solenoids.
 5. The apparatus of claim1 wherein the outer circumference surface (OBS) of the bulbousprotrusion (B) has a diameter that is between about 0.01 and about 0.20mm less than the throat diameter (TD) and the flow restriction gap (G)is between 0.05 and 0.2 mm.
 6. The apparatus of claim 1 wherein thedistal tip end of the valve pin is configured to close the gate and stepthe flow of injection fluid through the gate.
 7. The apparatus of claim1 wherein the valve pin has a narrowed neck or neck portion (N) that hasa diameter such that when the neck portion N is axially aligned with theaxis (AX) of the fluid flow channel a widened gap (WG) is formed betweenan outer circumferential surface (NS) of the neck (N) and the innercircumferential surface (TS) of the throat (T) that enables fullvelocity flow of the injection fluid material through the widened gap(WG) downstream toward and through the gate.
 8. The apparatus of claim 1wherein the valve pin includes an upstream portion configured or adaptedto stop flow of injection fluid through the flow channel when the valvepin is in the fully downstream position.
 9. The apparatus of claim 1wherein in the start of cycle position the bulbous protrusion and thethroat enable a restricted flow of the injection fluid from an upstreamside of the bulbous protrusion to a downstream side of the bulbousprotrusion that reduces tensile forces on the pin.
 10. The apparatus ofclaim 1 wherein the actuator is interconnected to a controller thatincludes a program that instructs the actuator to dispose the valve pinat the start of cycle such that the outer circumferential surface (IDS)is axially aligned with the throat (T).
 11. The apparatus of claim 1wherein the actuator is drivable at a rate of travel between zero and amaximum rate of travel, the actuator being interconnected to acontroller that includes a program that instructs the actuator to drivethe valve pin downstream from the start of cycle position to the fullydownstream position defining a stroke length, the program includinginstructions that instruct the actuator to drive the valve pindownstream at a rate of travel beginning from the start of cycleposition along at least a portion of the stroke length that is less thanthe maximum rate of travel.
 12. The apparatus of claim 1 wherein thebulbous protrusion (B) and the throat (T) are configured or adapted toenable a restricted flow of injection fluid that reduces a difference inpressure between fluid disposed upstream of the throat and fluiddisposed downstream of the throat when the bulbous protrusion and thethroat are axially aligned.
 13. A method of forming a part by operationof the apparatus of claim 1 comprising injecting an injection fluid fromthe injection molding machine into the manifold and controlling flow ofthe injection fluid into the cavity by use of a controller such that theactuator is instructed to drive the valve pin downstream from the startof cycle position to the fully downstream position at a rate of travelbeginning from the start of cycle position along at least a portion ofthe stroke length that is less than the maximum rate of travel.